[PATCH 02/10] oslib: add qemu_debugger_attached()

["Denis V. Lunev" <den@openvz.org>]

From: Denis V. Lunev <den@openvz.org>

Code that watches for a hang has to tell a hang apart from a debugger
stop, because under a debugger every thread stops and whatever liveness
signal the watcher samples stops changing with them.

Linux reports the tracer in /proc/self/status and Windows has
IsDebuggerPresent(). Answer false elsewhere, which leaves the caller
behaving as it did before the check.

Match the Linux field at the start of a line. The Name: line holds
fifteen characters of comm, enough to spell the field name and appear
ahead of the real one.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>
Cc: Zhao Liu <zhao1.liu@intel.com>
Cc: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Denis V. Lunev <den@openvz.org>
---
 include/qemu/osdep.h |  9 +++++++++
 util/oslib-posix.c   | 22 ++++++++++++++++++++++
 util/oslib-win32.c   |  5 +++++
 3 files changed, 36 insertions(+)

diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index 1ec5b42230..96afe09632 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -658,6 +658,15 @@ bool qemu_write_pidfile(const char *pidfile, Error **errp);
 
 int qemu_get_thread_id(void);
 
+/**
+ * qemu_debugger_attached:
+ *
+ * Returns true if a debugger is currently tracing this process. Meant for
+ * code that would otherwise mistake a debugger stop for a hang, and false
+ * on hosts where this cannot be determined.
+ */
+bool qemu_debugger_attached(void);
+
 /**
  * qemu_kill_thread:
  * @tid: thread id.
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index dc001da66d..4eb6a40628 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -112,6 +112,28 @@ int qemu_get_thread_id(void)
 #endif
 }
 
+bool qemu_debugger_attached(void)
+{
+#ifdef CONFIG_LINUX
+    static const char key[] = "TracerPid:";
+    g_autofree char *status = NULL;
+    const char *p = NULL;
+
+    if (!g_file_get_contents("/proc/self/status", &status, NULL, NULL)) {
+        return false;
+    }
+    while ((p = strstr(p ? p : status, key))) {
+        if (p == status || p[-1] == '\n') {
+            return atoi(p + sizeof(key) - 1) > 0;
+        }
+        p += sizeof(key) - 1;
+    }
+    return false;
+#else
+    return false;
+#endif
+}
+
 int qemu_kill_thread(int tid, int sig)
 {
 #if defined(__linux__)
diff --git a/util/oslib-win32.c b/util/oslib-win32.c
index 5f3e8f4d98..6663d83151 100644
--- a/util/oslib-win32.c
+++ b/util/oslib-win32.c
@@ -228,6 +228,11 @@ int qemu_get_thread_id(void)
     return GetCurrentThreadId();
 }
 
+bool qemu_debugger_attached(void)
+{
+    return IsDebuggerPresent();
+}
+
 char *
 qemu_get_local_state_dir(void)
 {
-- 
2.53.0